How does the Selenga River connect to the Yenisey River system?

The Selenga River connects to the Yenisey River system through a series of waterways that serve as the river's ultimate source. The Selenga River flows into Lake Baikal, which is the primary source of the Angara River. The Angara, in turn, is a major tributary that joins the Yenisey River.123

Because the Angara is highly regulated by Lake Baikal and carries a greater volume of water than the Yenisey at their confluence, it is sometimes considered the upper course of the main river rather than a mere tributary. When the Selenga-Baikal-Angara system is included as part of the total length, the Yenisey River extends to 3,442 miles (5,539 km), making it one of the largest river systems in the world.32